In order to make it possible for persons in wheelchairs to be passengers or drivers in vehicles, for example in so-called minibuses, docking systems are sometimes used. The purpose of the docking systems is to secure the wheelchair in the vehicle. The systems normally comprise a base unit that is mounted on the floor of the vehicle at the location of the driver's seat or any one of the passenger seats, after the ordinary seat has been removed from this location. The systems also comprise an engaging device that is mounted on the wheelchair. When the wheelchair is to be secured in the intended location, the wheelchair is driven into the vehicle and up to the base unit. The docking is normally thereafter achieved by the wheelchair being driven further forward so that a part of the chassis of the wheelchair is located over the base unit, whereupon the engaging device that projects downwards from the wheelchair engages with a locking mechanism in the base unit.
For reasons associated with road safety, it is of course of the greatest importance that these docking systems achieve a secure fixing of the wheelchair. This means that the fixing must be strong, so that the very large forces on the wheelchair that can arise in the event of a collision are unable to break the fixing and cause the wheelchair to become loose. In addition, the fixing should be a butt contact, that is, it should permit as little relative movement as possible between the wheelchair and the vehicle. The greater such relative movement that is possible, the greater the risk that the person in the wheelchair will hit the steering wheel, for example, or some other part of the vehicle in the event of a collision. In addition, with such a relative movement, there would be a risk of a recoil immediately after the moment of impact, that could cause serious injury to the person in the wheelchair. In addition, the large moving mass of the combined weight of the wheelchair and the person that would arise in the event of such a relative movement would cause an additional load on the engaging parts of the docking system, which could result in the fixing being broken.
An additional desirable characteristic of the docking systems is that the wheelchair's clearance above the ground should not be affected adversely when the wheelchair is to be used normally outside the vehicle. It is generally recognized that a good clearance is of the greatest importance for giving the person in the wheelchair good freedom of movement in both rural and urban environments. With previously-known docking systems, the engaging devices on the wheelchair often consist of an engaging nose or the like that is attached in such a way that it projects downwards from the chassis of the wheelchair, which reduces the clearance considerably and as a result restricts access to some locations.
Previously-Known Technology
U.S. Pat. No. 4,690,364 describes a device for securing a wheelchair in a vehicle. The device comprises a base unit that is fixed to the floor of the vehicle and that has a locking mechanism. The device also comprises an engaging nose that is attached to a wheelchair by means of a framework in such a way that it does not move. When the framework is screwed onto the chassis of the wheelchair, the engaging nose projects downwards in order to be able to engage with the locking mechanism in the base unit.
When the wheelchair has been docked, the total weight of the wheelchair and of the person who is sitting in the wheelchair is supported by the wheels of the wheelchair. As at least two of the wheels are provided with pneumatic tyres in order to provide a comfortable ride, this means that, in the docked position, the wheelchair is able to move slightly in relation to the base unit and the vehicle. This relative movement corresponds to the cushioning effect of the pneumatic tyres. With the device described in U.S. Pat. No. 4,690,364, a butt fixing is thus not achieved, which results in the problems described above.
Modern wheelchairs, for example electrically-operated wheelchairs for use outdoors, often have a considerably more sophisticated suspension system with link arms and gas springs or the like. Such a modern wheelchair suspension system has a greater cushioning effect, that is, it allows a larger movement of the seat of the wheelchair in relation to the surface upon which the wheelchair is standing, than that provided by pneumatic tyres alone. Accordingly, the abovementioned problems are made worse if the device described in U.S. Pat. No. 4,690,364 is used for securing modern wheelchairs.
Yet another problem with the device described in U.S. Pat. No. 4,690,364 is that the engaging nose that projects downwards and that is permanently attached to the wheelchair reduces the wheelchair's clearance considerably. There is thus a risk of the projecting nose hitting the surface upon which the wheelchair is travelling, both when moving indoors and outdoors and when travelling in both a rural and an urban environment. As a result, the freedom of movement that is provided to the person in the wheelchair is, of course, restricted.